Photoconductors are highly photosensitive in the visible region, and are widely used in various devices, such as copying machines, printers, etc. Most of the currently used photoconductors are produced by applying a photosensitive layer including an inorganic charge generating material selected from selenium, zinc oxide, cadmium sulfide and others as a main component to a conductive substrate. However, these inorganic charge generating materials are still unsatisfactory in photosensitivity, thermal stability, water resistance, durability and other physical properties required in copying machines and printers. For example, photoconductors using cadmium sulfide suffer from poor water resistance and durability, and photoconductors using zinc oxide have a problem in terms of low durability. Further, photoconductors using selenium and cadmium sulfide are limited in their production and handling.
In an effort to solve the problems of the inorganic charge generating materials, a great deal of research has been conducted on organic charge generating materials. Of these, oxytitanium phthalocyanine is widely used due to its superior photosensitivity, durability, thermal stability, etc.
Oxytitanium phthalocyanine is known to exist in various crystal forms. Representative crystal forms are alpha-form (B- or II-form), beta-form (A- or I-form), meta-form (C- or III-form), gamma-form (D- or IV-form), and the like. Of these, since the gamma-form oxytitanium phthalocyanine has better electrophotographic characteristics than the other forms, it is widely used as a charge generating material. Since oxytitanium phthalocyanine exhibits different electrophotographic characteristics depending on its X-ray diffraction patterns, oxytitanium phthalocyanine characterized by its X-ray diffraction patterns is protected by patents assigned to a number of manufacturing companies. U.S. Pat. No. 5,132,197 discloses oxytitanium phthalocyanine showing X-ray diffraction characteristic peaks at Bragg angles of 9.0°, 14.2°, 23.9°, and 27.1°. U.S. Pat. No. 5,194,354 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of: 7.2°, 14.2°, 24.0° and 27.2°; 7.4°, 10.9° and 17.9°; 7.6°, 9.7°, 12.7°, 16.2° and 26.4°; or 8.5° and 10.2°. U.S. Pat. No. 5,298,353 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of: 9.0°, 14.2°, 23.9° and 27.1°; or 7.4°, 9.2°, 10.4°, 11.6°, 13.0°, 14.3°, 15.0°, 15.5°, 23.4°, 24.1°, 26.2° and 27.2°. U.S. Pat. No. 5,593,805 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.4°, 10.2°, 12.5°, 15.0°, 16.3°, 18.3°, 22.4°, 24.2°, 25.2°, and 28.5°. U.S. Pat. No. 4,728,592 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.6°, 10.2°, 12.6°, 13.2°, 15.1°, 16.2°, 17.2°, 18.3°, 22.5°, 24.2°, 25.3°, 28.6°, 29.3°, and 31.5°. U.S. Pat. No. 5,252,417 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 9.5°, 14.3°, 18.0°, 24.0°, and 27.2°. U.S. Pat. No. 5,567,559 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of: 7.5°, 9.3°, 13.6°, 14.3°, 17.9°, 24.0°, 27.2° and 29.1°; or 7.4°, 9.5°, 11.6°, 13.6°, 14.3°, 17.9°, 24.0°, 27.2° and 29.1°. U.S. Pat. No. 6,284,420 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.3°, 9.4°, 14.0°, 24.1°, 25.7°, 27.2°, and 28.5°. U.S. Pat. No. 4,898,799 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 9.5°, 11.7°, 15.0°, 23.5°, 24.1°, and 27.3°. U.S. Pat. No. 4,994,339 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 9.6°, 11.7°, 24.1°, and 25.2°. U.S. Pat. No. 5,039,586 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 6.8°, 9.5°, 11.5°, 13.4°, 18.0°, 24.1°, and 27.3°. U.S. Pat. No. 4,664,997 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 9.3°, 10.6°, 13.2°, 15.1°, 15.7°, 16.1°, 20.8°, 23.3°, 26.3°, and 27.1°. U.S. Pat. No. 5,213,929 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.4°, 22.3°, 24.1°, 25.3°, 27.3°, and 28.5°. U.S. Pat. No. 5,972,551 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.4°, 9.4°, 9.7°, and 27.3°. U.S. Pat. No. 6,447,965 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 7.3°, 9.4°, 9.6°, 11.6°, 13.3°, 17.9°, 24.1°, and 27.2°. U.S. Pat. No. 5,350,844 discloses oxytitanium phthalocyanine showing X-ray diffraction peaks at Bragg angles of 6.8°, 9.2° 10.4°, 12.3°, 13.1°, 15.0°, 15.6°, 16.0°, 20.6°, 23.2°, 25.3°, 26.2°, 26.5°, and 27.1°. The oxytitanium phthalocyanine charge generating material prepared by the method of the present invention is characterized in that it shows X-ray diffraction characteristic peaks at Bragg angles of 7.2°, 9.6°, 11.7°, 12.7°, 13.4°, 14.1°, 14.8°, 18.0°, 18.4°, 22.3°, 24.1°, and 27.2°, the strongest peak at a Bragg angle of 27.2°, the second strongest peak at a Bragg angle of 9.6°, single peaks having no splitting at Bragg angles of 9.6° and 24.1°, and no diffraction peak at a Bragg angle of 26°˜28°. The Bragg angle used herein is a 2theta value and has an error range of ±0.2°.
Oxytitanium phthalocyanine is commonly synthesized by reacting 1,2-dicyanobenzene or 1,3-diiminoisoindoline as a main material with titanium tetrachloride or tetraalkoxy titanium as a titanium source in N-methylpyrrolidone, 1-chloronaphthalene or quinoline as a solvent at 160˜200° C. for 6˜12 hours, and purifying the obtained reaction product. The final product is strictly defined as “oxytitanium phthalocyanine in a crude state (hereinafter, referred to as an “oxytitanium phthalocyanine crude”)”. Japanese Patent No. 62-256865 describes a method for preparing oxytitanium phthalocyanine by using 1,2-dicyanobenzene and titanium tetrachloride, U.S. Pat. No. 4,971,877 describes a method for preparing oxytitanium phthalocyanine by using 1,3-diiminoisoindoline and tetraalkoxy titanium, and Bull. Chem. Soc. Jpn., 68, 1001-1005, 1995 reports a method for preparing oxytitanium phthalocyanine by using 1,2-dicyanobenzene and tetrabutoxytitanium. Since the oxytitanium phthalocyanine crudes cannot be directly used as charge generating materials due to their large particle size and poor electrophotographic characteristics, they must undergo an appropriate post treatment process in order to be used as highly photosensitive charge generating materials. The structural formula of oxytitanium phthalocyanine is represented by the following Formula 1:

A representative post-treatment process of an oxytitanium phthalocyanine crude is one wherein the oxytitanium phthalocyanine crude is dissolved in concentrated sulfuric acid or hyperchlorinated carboxylic acid, recrystallized from various organic solvents, such as water, and treated with a halogenated aromatic solvent, such as a halobenzene or halonaphthalene, to prepare an oxytitanium phthalocyanine charge generating material. U.S. Pat. No. 5,164,493 describes a method for preparing oxytitanium phthalocyanine by using concentrated sulfuric acid and chlorobenzene. U.S. Pat. No. 5,252,417 describes a method for preparing oxytitanium phthalocyanine by using trifluoroacetic acid and chlorobenzene. U.S. Pat. No. 5,786,121 describes a method for preparing oxytitanium phthalocyanine by using pentafluoropropionic acid and chlorobenzene. U.S. Pat. No. 6,521,387 describes a method for preparing oxytitanium phthalocyanine by using concentrated sulfuric acid and 1,2-dichloroethane. U.S. Pat. No. 5,773,184 describes a method for preparing oxytitanium phthalocyanine by using difluoroacetic acid or dichloroacetic acid.
Another representative post-treatment process of an oxytitanium phthalocyanine crude is one wherein the oxytitanium phthalocyanine crude is dry-ground using a grinder, such as a ball mill, vibration mill or attritor, and is then treated with organic solvents. U.S. Pat. No. 5,567,559 describes a method for preparing oxytitanium phthalocyanine by using a ball mill and n-butyl ether, and U.S. Pat. No. 5,059,355 describes a method for preparing oxytitanium phthalocyanine by using a paint shaker and 1,2-dichlorobenzene.
The oxytitanium phthalocyanine charge generating materials are advantageous in terms of their superior electrophotographic characteristics, but have a disadvantage of poor crystal instability in organic solvents, e.g., tetrahydrofuran. Due to this disadvantage, when the oxytitanium phthalocyanine is used to prepare a coating solution for a charge generating layer, the storage stability is extremely deteriorated, leading to a shortened shelf life. In addition, when the oxytitanium phthalocyanine is dissolved in an acid or ground, followed by the treatment with an organic solvent, it is highly sensitive to temperature and thus a considerable care must be taken to control the temperature in the treatment with the organic solvent. It appears that because the crystal form of the oxytitanium phthalocyanine is not completely transformed into gamma-form and a small quantity of beta- or alpha-form crystal remains, the previously formed gamma-form crystal is easily transformed into the more stable beta- or alpha-form crystal.